Method Of Controlling A Powered Air Purifying Respirator

ABSTRACT

There is provided a method of controlling a powered air purifying respirator blower system to deliver a substantially uniform volumetric airflow to a user, the system comprising a fan powered by a battery in communication with a variable speed electric motor, the variable speed electric motor is controlled by an electronic control unit for delivering a forced flow of air through at least one filter to a user, comprising the steps of: (a) determining an estimated system run time by summing a battery run time remaining and a system run time; and (b) altering a speed of the variable speed electric motor when the estimated system run time is equal to or less than a desired system run time.

FIELD

The present invention relates to a blower system, and method ofcontrolling a blower system, for use in a powered air purifyingrespirator (PAPR).

BACKGROUND

When working in areas where there is known to be, or there is a risk ofthere being, dusts, fumes or gases that are potentially hazardous orharmful to health, it is usual for the worker to use a respirator. Acommon type of respirator used in such circumstances is a powered airpurifying respirator (PAPR). A PAPR has a blower system comprising a fanpowered by an electric motor for delivering a forced flow of air to therespirator user. A turbo unit is a housing that typically contains theblower system, and is adapted to connect a filter to the blower system.Air is drawn through the filter by the blower system and passed from theturbo unit through a breathing tube to a headpiece, for example, ahelmet or headtop, thus providing filtered air to the user's breathingzone (the area around their nose and mouth). A blower system for a PAPRmay also include an electronic control unit to regulate the powerdriving the fan. Typically, a single power supply, for example abattery, provides power for both the fan and the electronic controlunit.

The electronic control unit can be used, for example, to control thepower to the electric motor with the aim of maintaining a substantiallyuniform volumetric airflow from the blower. The term “volumetric airflow” indicates the volume of air provided to a user at any one time asopposed to the mass of air provided to a user any one time. Sufficientairflow is required by the user to ensure that the designated level ofrespiratory protection is maintained. However, too high an airflow cancause discomfort and excessive cooling to the user's head inside theheadpiece. Too low an airflow can cause ingress of contaminants into theuser's breathing zone. The electronic control unit may also be used totrigger alarms to the user, for example, to alert the user if theairflow falls below a designated level, or to alert the user that thefilters may be blocked with dust and need to be replaced. It haspreviously been proposed to control the power to the fan motor of a PAPRblower system in dependence on a combination of motor voltage, motorcurrent and motor speed. Examples of blower control systems of that typeare described in US 2008/0127979 (Becker et al.) and U.S. Pat. No.7,244,106 (Kallman et al.).

US 2008/0127979 describes an electronic control system using a pulsewidth modulation (PWM) ratio as a control variable to generate aspecific motor speed and a respective airflow. The PWM ratio is readfrom a calibration curve stored in the electronic control system.

U.S. Pat. No. 7,244,106 describes a control unit that detects the powerconsumption of the motor and the speed of the fan and compares this witha characteristic curve, stored in a memory, for the motor for a givenairflow from the fan. In the event of a deviation from thischaracteristic curve, the control unit regulates a change in the voltagesupplied to the motor to maintain a constant airflow.

A predetermined volumetric airflow of filtered air is usually intendedto be delivered to the user of a PAPR to give a certain level ofprotection from the ingress of particles or gases into their breathingzone. Currently available systems often provide a volumetric airflowthat is much higher than is actually needed, rather than risk asituation where too little air is provided. A higher airflow usuallymeans that the battery life between charges is reduced or that largerbatteries are required, as more power is consumed to provide the higherairflow. Filter life is also reduced by providing a higher airflow asexcess contaminated air is moved through the filters leading tounnecessary filtering and premature clogging or saturation of thefilters. As filters are consumable and require replacement many timesover the lifetime of the PAPR, this can lead to higher running costs. Afurther problem is that in many PAPRs a low airflow alarm is required,alerting the user to the fact that the airflow has fallen below apredetermined level. Where an inaccurate airflow measuring or controlsystem is used, the alarm level is often set at an artificially highlevel to ensure that the user is always safe. This in turn can lead tofilters being changed too frequently or the user leaving the workplaceunnecessarily. Hence it can be seen that more accurate control of theairflow at a particular volumetric airflow can lead to improved batterylives between charges or the use of smaller and lighter batteries,improved filter life and reduction of premature low airflow alarms. Allof these factors can also lead to the improved productivity of the user.

US 2012/0138051 (Curran) describes a method of controlling a powered airpurifying respirator blower to deliver a substantially uniformvolumetric airflow to a user by taking into consideration one or moreambient air characteristics when controlling the blower.

Conventional PAPRS, having flow control, stay at a constant flow ratethroughout the filter loading or battery range. This type of flowcontrol enables the use of multiple control airflow rates in a PAPR.Users can decide to run at high airflow or low airflow. A typical userwants to run at higher airflow rate for as long as possible to aid incooling. If a user is in a high filter loading environment, however, thehigh airflow rate will result in shorter filter life and shorter batterylife, resulting in shorter system run times. One way this is dealt withis to provide PAPRs with large filters and large batteries to enablestandard run times of typically 250 minutes).

It is desirable therefore to use a method of controlling a PAPR thatminimizes such issues while maintaining or improving the overallfunctionality of the PAPR. It is also desirable to provide a method thatensures users will obtain at least 250 minutes of use from a fullycharged battery.

SUMMARY

The present invention aims to address these problems by providing amethod that ensures users of a powered air purifying respirator willobtain at least 250 minutes of use from a fully charged battery bymonitoring battery life and automatically adjusting airflow rate toreduce power drawn from the battery when battery life is diminished.

In one aspect, the present invention provides a method of controlling apowered air purifying respirator blower system to deliver asubstantially uniform volumetric airflow to a user, the systemcomprising a fan powered by a battery in communication with a variablespeed electric motor, the variable speed electric motor is controlled byan electronic control unit for delivering a forced flow of air throughat least one filter to a user, comprising the steps of: (a) determiningan estimated system run time by summing a battery run time remaining anda system run time; and (b) altering a speed of the variable speedelectric motor when the estimated system run time is equal to or lessthan a desired system run time.

In some embodiments altering the speed of the variable speed electricmotor is decreasing the speed of the variable speed electric motor. Insome embodiments, decreasing the speed of the variable speed electricmotor increases the battery run time remaining.

In some embodiments, the method further comprises, before step (a),determining a speed of the variable speed electric motor andestablishing an electrical characteristic applied by the electroniccontrol unit to the variable speed electric motor. In some embodiments,the method further comprises step (c) altering the speed of the variablespeed electric motor to a speed lower than the speed established in step(b) by establishing and applying a new electrical characteristic to thevariable speed electric motor.

In some embodiments, the substantially uniform volumetric airflow fromthe fan is varied based on the speed of the electric motor. In someembodiments, the substantially uniform volumetric airflow from the fanis variable and chosen from any one of a number of pre-selected airflowvalues. In some embodiments, the substantially uniform volumetricairflow from the fan is variable and chosen from an unlimited number ofairflow values. In some embodiments, the battery comprises a batterymanagement circuit.

The above summary of the present disclosure is not intended to describeeach embodiment of the present invention. The details of one or moreembodiments of the invention are also set forth in the descriptionbelow. Other features, objects, and advantages of the invention will beapparent from the description and from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

By way of example only, embodiments of the invention will now describedbelow with reference to the accompanying drawings, in which:

FIG. 1 is a diagrammatical illustration of a powered air purifyingrespirator;

FIG. 2 shows a block diagram of a blower system according to a firstembodiment of the present disclosure; and

FIG. 3 is a flow chart illustrating an exemplary step down algorithmuseful for controlling the presently disclosed powered air purifyingrespirator.

DETAILED DESCRIPTION

Before any embodiments of the invention are explained in detail, it isto be understood that the invention is not limited in its application tothe details of construction and the arrangement of components set forthin the following description. The invention is capable of otherembodiments and of being practiced or of being carried out in variousways. Also, it is to be understood that the phraseology and terminologyused herein is for the purpose of description and should not be regardedas limiting. The use of “including,” “comprising,” or “having” andvariations thereof herein is meant to encompass the items listedthereafter and equivalents thereof as well as additional items. Anynumerical range recited herein includes all values from the lower valueto the upper value. For example, if a percentage is stated as 1% to 50%,it is intended that values such as 2% to 40%, 10% to 30%, or 1% to 3%,etc., are expressly enumerated. These are only examples of what isspecifically intended, and all possible combinations of numerical valuesbetween and including the lowest value and the highest value enumeratedare to be considered to be expressly stated in this application.

In the present detailed description of the preferred embodiments,reference is made to the accompanying drawings, which illustratespecific embodiments in which the invention may be practiced. Theillustrated embodiments are not intended to be exhaustive of allembodiments according to the invention. It is to be understood thatother embodiments may be utilized and structural or logical changes maybe made without departing from the scope of the present invention. Thefollowing detailed description, therefore, is not to be taken in alimiting sense, and the scope of the present invention is defined by theappended claims.

Unless otherwise indicated, all numbers expressing feature sizes,amounts, and physical properties used in the specification and claimsare to be understood as being modified in all instances by the term“about.” Accordingly, unless indicated to the contrary, the numericalparameters set forth in the foregoing specification and attached claimsare approximations that can vary depending upon the desired propertiessought to be obtained by those skilled in the art utilizing theteachings disclosed herein.

As used in this specification and the appended claims, the singularforms “a,” “an,” and “the” encompass embodiments having pluralreferents, unless the content clearly dictates otherwise. As used inthis specification and the appended claims, the term “or” is generallyemployed in its sense including “and/or” unless the content clearlydictates otherwise.

Spatially related terms, including but not limited to, “proximate,”“distal,” “lower,” “upper,” “beneath,” “below,” “above,” and “on top,”if used herein, are utilized for ease of description to describe spatialrelationships of an element(s) to another. Such spatially related termsencompass different orientations of the device in use or operation inaddition to the particular orientations depicted in the figures anddescribed herein. For example, if an object depicted in the figures isturned over or flipped over, portions previously described as below orbeneath other elements would then be above or on top of those otherelements.

As used herein, when an element, component, or layer for example isdescribed as forming a “coincident interface” with, or being “on,”“connected to,” “coupled with,” “stacked on” or “in contact with”another element, component, or layer, it can be directly on, directlyconnected to, directly coupled with, directly stacked on, in directcontact with, or intervening elements, components or layers may be on,connected, coupled or in contact with the particular element, component,or layer, for example. When an element, component, or layer for exampleis referred to as being “directly on,” “directly connected to,”“directly coupled with,” or “directly in contact with” another element,there are no intervening elements, components or layers for example. Thetechniques of this disclosure may be implemented in a wide variety ofcomputer devices, such as servers, laptop computers, desktop computers,notebook computers, tablet computers, hand-held computers, smart phones,and the like. Any components, modules or units have been described toemphasize functional aspects and do not necessarily require realizationby different hardware units. The techniques described herein may also beimplemented in hardware, software, firmware, or any combination thereof.Any features described as modules, units or components may beimplemented together in an integrated logic device or separately asdiscrete but interoperable logic devices. In some cases, variousfeatures may be implemented as an integrated circuit device, such as anintegrated circuit chip or chipset. Additionally, although a number ofdistinct modules have been described throughout this description, manyof which perform unique functions, all the functions of all of themodules may be combined into a single module, or even split into furtheradditional modules. The modules described herein are only exemplary andhave been described as such for better ease of understanding.

The term “altering” as used herein means automatically increasing ordecreasing the air flow rate of the PAPR.

Each of the embodiments described below employ a turbo as shown inFIG. 1. FIG. 1 is a diagrammatical illustration of a powered airpurifying respirator. The PAPR comprises a headpiece 1, a turbo unit 2,a breathing tube 3, a filter 4 and a belt 5. Headpiece 1 is worn on theuser's 6 head. It at least partially encloses the user's 6 head to forma breathing zone 7, that is, the area around their nose and mouth, sothat the filtered air is directed to this breathing zone 7. Turbo unit 2may be attached to a belt 5 to enable it to be secured about the user's6 torso. Turbo unit 2 houses a blower system (not shown), which drawsthe air through the PAPR system using a fan (also not shown). Turbo unit2 supplies air to headpiece 1 through breathing tube 3, which isconnected between outlet 8 of turbo unit 2 and inlet 9 of headpiece 1.Turbo unit 2 is fitted with a filter 4, which can be either inside turbounit 2 or attached to turbo unit 2 as shown in FIG. 1 such that filter 4is in an airflow path, preferably disposed upstream of a fan opening ofthe blower. The purpose of providing filter 4 is to remove particlesand/or gases and/or vapours from the ambient air before the air isdelivered to user 6. A battery pack 10, which is fitted to turbo unit 2provides power to an electronic control unit 23 and to a motor 22 (bothshown in FIG. 2 as discussed below).

Headpiece 1 may have a variety of configurations. Although a hood isillustrated in FIG. 1, headpiece 1 could be a helmet, a mask, or a fullsuit, provided it covers at least the orinasal area of the user's face,to direct air to user's 6 breathing zone 7. Full face respirators orhalf face mask respirators may be used as headpieces in conjunction withthe embodiment of the present invention. Alternative ways of supportingturbo unit 2 on a user's 6 body or otherwise are also within the scopeof the present disclosure. For example, a backpack-type support may beprovided for turbo unit 2.

Generally when using a helmet or hood in a PAPR, a higher constantairflow is desired, than when a mask is used. Where user 6 may changebetween helmets and masks, or where the turbo unit 2 is shared betweenmultiple users, it is desirable to have a range of substantially uniformvolumetric airflows. The range of substantially uniform volumetricairflows may be continuously variable between a first airflow rate and asecond airflow rate, or may be a series of discrete steps between thefirst and second airflow rates. For example, a system may be set to afirst predetermined airflow value for use with a helmet or hood to asecond, lower predetermined airflow value for use with a mask.

A PAPR may also be designed with smaller and lighter batteries, andsmaller and lighter or lower profile filters. Turbo unit 2 may be fittedwith more than one filter 4 in the airflow path, to remove particlesand/or gases and vapours from the ambient air before the air isdelivered to user 6. Filter(s) 4 may be inside turbo unit 2 or fitted tothe outside of turbo unit 2. Battery 10, may be attached to turbo unit 2as illustrated in FIG. 1 or may be remote from turbo unit 2 andconnected by a suitable cable.

The following illustrates how the blower system in accordance with someembodiments of the present disclosure may operate. In the followingexamples, the structural components of the PAPR may be assumed to be asdescribed above with reference to FIGS. 1 and 2.

FIG. 2 shows a block diagram of a blower system according to a firstembodiment of the present disclosure. The blower system is housed withinturbo unit 2 as, for example, illustrated in FIG. 1. In someembodiments, a blower 20 includes a housing 17 having an inlet 18 and anoutlet 19. Blower 20 includes a fan 21, having a plurality of blades 16,driven by a motor 22. Blower 20 is controlled by electronic control unit23, which regulates the power provided from a power source (such asbattery 10 as depicted in FIG. 1) to motor 22. In some embodiments, thepower source is a battery, an electric cord that can be plugged into apower outlet, a solar cell, and the like. In some embodiments, apreferred power source is a battery containing gas gauging circuitry,such as batteries that use standard System Management Bus (“SMBus”)communications to provide an input 26 to microprocessor device 24.Exemplary commercially available SMBus gas gauges are available underthe trade designation “TI BQ20Z90” from Texas Instruments Inc. Dallas,Tex. USA. In some embodiments, the power supplied from power supply tomotor 22 is an electrical characteristic, such as for example, voltage.

It is desirable that a substantially uniform volumetric airflow besupplied to a user's 6 breathing zone 7, such that when user 6 inhales,sufficient filtered air is available for user 6 to breathe easily andnormally, and no potentially contaminated ambient air is inhaled. Asubstantially uniform volumetric airflow is preferably, but not limitedto, an airflow rate where the deviation from the desired orpredetermined airflow is in the range −15 to +15 litres per minute.

In order to achieve a substantially uniform volumetric airflow at aparticular volumetric airflow rate, either the airflow must be known ora correlation between various operating parameters and the requiredairflow must be known. It is possible to monitor the volumetric airflowby using a discrete airflow sensor. However, in the present disclosure,it has been appreciated that various operating parameters of fan 21 andmotor 22 including fan or motor speed, motor voltage, motor current andmotor power can be used to determine the volumetric airflow as describedbelow.

With further reference to FIG. 2, the blower system comprises electroniccontrol unit 23 that functions to maintain a substantially uniform,preferably constant, volumetric airflow to headpiece 1. Electroniccontrol unit 23 comprises: a microprocessor device 24, such as a singlechip microcontroller, for computing information; a memory device 25,such as flash RAM, for storing information; inputs to microcontrollerinclude data from sensors such as motor current sensors and fan speedsensors 28, battery gas gauge 26 and voltage provided by battery 10; andan output controller 27, such as a pulse width modulation controllerchip, for providing power to motor 22 and any alarm or statusindicators, such as buzzers or light emitting diodes, that may beincluded in the PAPR. Memory device 25 of electronic control unit 23 hastwo parts: a fixed memory and a temporary memory. The fixed memory ispopulated with data, for example, at the time of manufacture, comprisingthe algorithms and programs for enabling microprocessor 24 to carry outits calculations and procedures, and calibration information from thefactory calibration procedure. The temporary memory is used for storingdata and information such as sensor readings and fan operating parameterdata collected during start-up and running of turbo unit 2. If desired,this data maybe erased when turbo unit 2 is powered down.

In some embodiments, a three-phase square-wave, brushless, directcurrent motor 22 may be used to drive fan 21 of blower 20. The equationsbelow, EQ.1, EQ.2 and EQ.3 are well known and show the relationshipsbetween the main parameters of such a motor.

$\begin{matrix}{T = {k_{T}I}} & \left( {{Eq}.\mspace{14mu} 1} \right) \\{E = {k_{E}\frac{2\mspace{14mu} \pi}{60}n}} & \left( {{Eq}.\mspace{14mu} 2} \right) \\{V_{s} = {E + {R_{m}I}}} & \left( {{Eq}.\mspace{14mu} 3} \right)\end{matrix}$

-   -   T Air gap torque (mNm)    -   k_(T) Torque constant (mNm/A)    -   I Motor current (A)    -   E Back EMF (V)    -   k_(E) Back EMF constant (Vs/rad)    -   n Speed (rpm)    -   V_(s) Applied motor voltage (V)    -   R_(m) Winding resistance (Ω)

Motor 22 used in the embodiments described above is a three-phasesquare-wave brushless direct-current motor. Alternatively, a segmentedcommutator brushed direct current motor may be used. Equations EQ.1,EQ.2 and EQ.3 are known to be true for both the brushed and brushlesstypes of motors. Consequently, most types of direct current motors knownwithin the respirator industry could be used in presently disclosedblower 20. Other non-direct current types of motors that are known forPAPR applications may also be used. Alternative motor control methods,such as pulse width modulation are also envisaged as being within thescope of the present invention.

As explained above, blower 20 comprises a fan 21, which is used to moveair through filter(s) 4 and deliver it to user 6. Fan 21 illustrated inthe drawings is of the type often known as a centrifugal or radial fan,meaning that the air enters the fan in the direction of the fan axis andexits in a radial direction to the fan.

Still referring to FIG. 2, fan speed is measured by means of a sensor 28fitted to blower 20 that measures the number of revolutions of fan 21 ina given time. A suitable type of sensor for measuring the fan speedwould be a Hall effect device, although other types of sensor could beused. The fan speed 28 information is received by microprocessor device24 of electronic control unit 23. Output to controller 27 can be voltageapplied to electric motor 22.

In some embodiments, air should be delivered to user 6 at apredetermined substantially uniform volumetric airflow. In certaincircumstances, however, user 6 may need to be able to adjust the airflowto a different level. For example if user 6 is working particularly hardand breathing more deeply or at a faster rate than usual, they maydesire to increase the airflow. To enable this, in some embodiments,electronic control unit 23 is provided with a discrete range of two,three or more different, pre-set airflow values, for example, preferably185 actual liters per minute, more preferably 205 actual liters perminute and most preferably 225 actual liters per minute for a hood orhelmet, and preferably 135 actual liters per minute, more preferably 150actual liters per minute and most preferably 170 actual liters perminute for a mask. In some embodiments, electronic control unit 23 isprovided with an algorithm that allows continuous monitoring and varyingof the airflow rate at various airflow values. However, electroniccontrol unit 23 is usually set such that it is not possible for user 6to inadvertently reduce the airflow below a level where the minimumprotection is given.

Referring now to FIG. 3, a method 30 is shown that ensures users of apowered air purifying respirator will obtain at least 250 minutes of usefrom a fully charged battery by monitoring battery life andautomatically adjusting airflow rate to reduce power drawn from thebattery when battery life is diminished. Method 30 is run withinpreviously disclosed electronic microprocessor device 23 and used tocontrol motor 22, which is in communication with fan 21 and battery pack10. Method 30 provides a step 32 for determining whether air flow rateis stabilized. For example, a useful method may use a timer and apredetermined time during which an original manufacturer's defined airflow speed is expected to stabilize or settle timer is expired. Forexample, a useful method may ask whether an air flow speed settle timerhas expired, after which the next step in the method is pursued.Referring again to FIG. 3, if air flow rate is not stabilized, presentlydisclosed method 30 will return to a main loop 46 step, bypassing therest of the method.

If air flow rate is stabilized, method 30 provides a second step 34 fordetermining whether a track time flag is set. This step ensures that thesystem is tracking system run time. If not, presently disclosed method30 will return to a main loop 46 step.

If a track time flag is set, method 30 provides a third step 36 fordetermining whether the presently running air flow speed is greater thanthe lowest speed possible for the system being run. If the presentlyrunning air flow speed is not greater than the lowest speed possible forthe system being run, presently disclosed method 30 will return to amain loop 46 step.

If a presently running air flow speed is greater than the lowest speedpossible for the system being run, method 30 provides a fourth step 38for determining if filter load is greater than a determined value. Insome embodiments, this step 38 is optional. In some embodiments, thedetermined value of the filter load is a predetermined value, such as afilter load of greater than 90 percent of the operational range per airflow rate. In some embodiments, usage data about filter load can bestored and accessed by microprocessor 24 module, such as in memorydevice 25. Usage data may include the length of time filter(s) 4 hasbeen worn by the user. Usage data may also include the length of timefilter(s) 4 has been in active use. Usage data can include a variety oftypes of information related to user's 6 wearing and use of filter(s) 4,the environment in which filter(4) have been used and stored, and otherinformation relating to its use. Any of these values can be used todetermine “filter load” value in step 38 of the presently disclosedmethod.

Referring again to FIG. 3, method 30 provides that, if filter load isnot greater than a determined value as determined in step 38, method 30provides a fifth step 40 of determining an estimated system run time(RunTimeTrack) by summing a battery run time remaining (RunTimetoEmpty)and a system run time (Time_On). If filter load is greater than adetermined value as determined in step 38, in some embodiments, method30 jumps to a subsequent step 44 of altering air flow speed, such as forexample decreasing or stepping down air flow speed, and starting an airflow speed settle timer. In some embodiments, air flow speed settletimer is set to a certain time value, such as, for example 1 minute, 2minutes, 3 minutes, 4 minutes, 5 minutes, 10 minutes, 15 minutes, andthe like. In some embodiments, air flow speed settle timer is not set toa specific time value or this step is completely omitted, which wouldalso obviate the need for step 32. In some embodiments, the air flowspeed may be decreased to a predetermined values as defined above. Thisstep may be repeated for which the decreases in air flow rate may beconducted in incremental, predetermined steps, which may be called“Stepped Down Flow Speed(s)”. In some embodiments, there can be 1, 2, 3,5 or more different incremental, predetermined steps for decreasing airflow rate. In some embodiments, there can be an unlimited number ofdifferent incremental, predetermined steps for decreasing air flow rate.In some embodiments, altering air flow speed may include increasing airflow speed. In some embodiments, altering air flow speed may includeboth decreasing and increasing air flow speed. For example, in someembodiments, air flow is monitored and controlled in real time accordingto method 30.

Referring again to FIG. 3, once estimated system run time (RunTimeTrack)is determined in step 40, method 30 provides step 42 in which estimatedrun time is compared to a desired run time. For example, if a desiredrun time is 250 minutes, step 42 determines whether the estimated systemrun time (RunTimeTrack) is less than 250 minutes. If estimated systemrun time (RunTimeTrack) is not less than 250 minutes method 30 returnsto main loop 46. If estimated system run time (RunTimeTrack) is lessthan 250 minutes, method 30 advances to step 44, as previouslydisclosed, for altering air flow speed, such as for example decreasingor stepping down air flow speed, and starting an air flow speed settletimer. Once step 44 is complete, method 30 returns to main loop 46.

If implemented in software, the techniques may be realized at least inpart by a computer-readable medium comprising instructions that, whenexecuted in a processor, performs one or more of the methods describedabove. The computer-readable medium may comprise a tangiblecomputer-readable storage medium and may form part of a computer programproduct, which may include packaging materials. The computer-readablestorage medium may comprise random access memory (RAM) such assynchronous dynamic random access memory (SDRAM), read-only memory(ROM), non-volatile random access memory (NVRAM), electrically erasableprogrammable read-only memory (EEPROM), FLASH memory, magnetic oroptical data storage media, and the like. The computer-readable storagemedium may also comprise a non-volatile storage device, such as ahard-disk, magnetic tape, a compact disk (CD), digital versatile disk(DVD), Blu-ray disk, holographic data storage media, or othernon-volatile storage device.

The term “processor,” or “controller” as used herein may refer to any ofthe foregoing structure or any other structure suitable forimplementation of the techniques described herein. In addition, in someaspects, the functionality described herein may be provided withindedicated software modules or hardware modules configured for performingthe techniques of this disclosure. Even if implemented in software, thetechniques may use hardware such as a processor to execute the software,and a memory to store the software. In any such cases, the computersdescribed herein may define a specific machine that is capable ofexecuting the specific functions described herein. Also, the techniquescould be fully implemented in one or more circuits or logic elements,which could also be considered a processor.

Various modifications and alterations of this invention will becomeapparent to those skilled in the art without departing from the scopeand spirit of this invention.

1. A method of controlling a powered air purifying respirator blowersystem to deliver a substantially uniform volumetric airflow to a user,the system comprising a fan powered by a battery in communication with avariable speed electric motor, the variable speed electric motor iscontrolled by an electronic control unit for delivering a forced flow ofair through at least one filter to a user, comprising the steps of: (a)determining an estimated system run time by summing a battery run timeremaining and a system run time; and (b) altering a speed of thevariable speed electric motor when the estimated system run time isequal to or less than a desired system run time.
 2. The method of claim1, wherein altering the speed of the variable speed electric motor isdecreasing the speed of the variable speed electric motor.
 3. The methodof claim 2, wherein decreasing the speed of the variable speed electricmotor increases the battery run time remaining.
 4. The method of claim1, further comprising, before step (a), determining a speed of thevariable speed electric motor and establishing an electricalcharacteristic applied by the electronic control unit to the variablespeed electric motor.
 5. The method of claim 1, further comprising step(c) altering the speed of the variable speed electric motor to a speedlower than the speed established in step (b) by establishing andapplying a new electrical characteristic to the variable speed electricmotor.
 6. The method of claim 5, wherein the substantially uniformvolumetric airflow from the fan is varied based on the speed of theelectric motor.
 7. The method of claim 5, wherein the substantiallyuniform volumetric airflow from the fan is variable and chosen from anyone of a number of pre-selected airflow values.
 8. The method of claim5, wherein the substantially uniform volumetric airflow from the fan isvariable and chosen from an unlimited number of airflow values.
 9. Themethod of claim 1, wherein the battery comprises a battery managementcircuit.